Field of the Invention
The present invention relates to exposure apparatuses, exposure methods, and device manufacturing methods, and more particularly to an exposure apparatus and an exposure method used in a lithography process for manufacturing electronic devices, and a device manufacturing method using the exposure apparatus and the exposure method.
Description of the Background Art
Conventionally, in a lithography process for manufacturing electronic devices (micro-devices) such as semiconductor devices (such as ICs) and liquid crystal display devices, sequential-moving type projection exposure apparatuses are mainly used, such as a projection exposure apparatus of a step-and-repeat method (a so-called stepper) and a projection exposure apparatus of a step-and-scan method (a so-called scanning stepper (also called a scanner)).
With these type of exposure apparatuses, a pattern formed on a mask or a reticle (hereinafter referred to collectively as a “reticle”) is transferred on each of a plurality of shot areas on an object such as a wafer or a glass plate (hereinafter referred to collectively as a “wafer”) coated with a sensitive agent (a resist), via a projection optical system.
Since these types of projection exposure apparatuses are used to manufacture micro-devices, to make the device serving as an end product have a desired performance, it is important to be able to accurately overlay and form a reduced image of the pattern formed on the reticle (referred to as the exposure pattern) corresponding to the projection magnification of the projection optical system on the pattern actually formed in each shot area on the wafer (referred to as the base pattern); that is, the overlay accuracy is important.
However, in the actual exposure sequence, exposure operation is performed through a wafer alignment mark formed on the wafer in a predetermined positional relation with each shot area and a reticle alignment mark formed on the reticle in a predetermined positional relation with the exposure pattern, presuming that the alignment marks represent the position of the pattern (e.g., refer to U.S. Pat. No. 5,646,413). In this manner, the position of the actual pattern is indirectly presumed from the position of the alignment marks.
The above presumption stands for the reason below. For example, in the case of the reticle side, since the reticle alignment mark and the exposure pattern are drawn simultaneously with an electron-beam exposure apparatus on the same glass substrate (reticle blank), the positional relation between the reticle alignment mark and the exposure pattern is secured to a drawing error level of the electron-beam exposure apparatus. Accordingly, the position of the exposure pattern whose positional relation with the reticle alignment mark is known can be presumed favorably when detection (measurement) of the position of the reticle alignment mark is performed.
The above presumption, however, is made on the premise that the position of the exposure pattern and the reticle alignment mark do not change, therefore the presumption may not actually stand. The most common example can be the case when a variation (distortion) occurs in the exposure pattern due to thermal deformation (such as thermal expansion) of the reticle by irradiation of the exposure light. Normally, reticle alignment (alignment of the reticle or position measurement for the alignment) is performed, using the reticle alignment mark located at four points in the periphery of the reticle. In this reticle alignment, however, only magnification change in the X-axis direction and the Y-axis direction and linear components such as orthogonality and rotation are obtained, in addition to positional information in a surface of the exposure pattern (for example, within the XY plane). That is, information cannot be obtained of non-linear shape change that occurs in the reticle due to heat absorption (e.g., shape change to a shape that resembles a map symbol of a bank, or to a shape of a barrel).
Drawing more reticle alignment marks at places in the periphery of the exposure pattern on the reticle blank, and measuring the marks at the time of reticle alignment allow a more accurate approximation, since the outer periphery shape of the exposure pattern can be recognized. In this case, however, in addition to requiring time for measurement which greatly reduces the throughput, errors occur in the presumption when distortion (deformation state) of the periphery of the pattern area of the exposure pattern and distortion of the actual pattern within the pattern area do not have a proportional relation. The influence is especially great, for example, such as when the shot size is not full-field and the width or total length of the shot is small, or when the transmittance distribution within the reticle pattern area is uneven.